1. Field of the Invention
The present invention relates generally to a system for conditioning a polishing surface, such as the surface of a web-shaped polishing pad. The invention also relates to rollers and other devices for applying different conditioning treatments to different portions of a polishing surface. The term xe2x80x9cpolishingxe2x80x9d is used broadly herein to include planarizing and other mechanical and chemical-mechanical procedures for producing smooth surfaces.
2. Discussion of the Related Art
Systems for polishing semiconductor wafers and the like are well known. In a conventional process, a surface of a semiconductor wafer is mechanically scoured by a conformable polishing pad. A chemical slurry may be used in conjunction with the polishing pad to provide a high material removal rate and/or improved surface planarization.
In a typical chemical-mechanical planarization (xe2x80x9cCMPxe2x80x9d) process, relative movement between a semiconductor substrate and a wetted pad causes material to be chemically and physically polished from the substrate surface. Chemical-mechanical planarization is used to prepare wafers for integrated circuits, and to planarize substrates on which one or more layers have been deposited and etched.
Referring now to FIG. 1, it has been suggested to provide a polishing apparatus 20 with a continuous web-shaped polishing pad 22. The pad 22 may be formed of a non-abrasive polymeric material, such as woven polyurethane, or other suitable materials. The pad 22 is movably supported on a workstation table 24. Guide rollers 26, 28 stretch the pad 22 over the table 24 in the illustrated position.
In operation, a carrier 30 presses a work piece, such as a semiconductor substrate 32, against the pad surface 34. The carrier 30 also rotates the substrate 32 around first and second parallel axes. Abrasive particles and/or chemicals in a planarizing slurry (not illustrated) assist in the removal of material from the surface of the substrate 32. The slurry may be dispensed through suitable nozzles (not illustrated).
Over time, the surface 34 of the web-shaped pad 22 becomes xe2x80x9cglazed.xe2x80x9d The glazed condition may be caused by spent slurry accumulating in the porous pad surface 34. In addition, the pressure applied by the carrier 30 tends to compress the pad 22. As the pad 22 becomes glazed, its coefficient of friction is reduced and becomes non-uniform, resulting in a lower material removal rate and/or poor quality control. Glazing of the pad surface 34 may increase the time required to polish each substrate 32. In addition, such glazing may make it difficult to obtain the desired substrate planarity.
For these and other reasons, the pad 22 may be provided on a supply roller 52. The supply roller 52 carries an unused or pre-operative portion of the pad 12. A motor (not shown in FIG. 1) advances the pad 22 intermittently in the direction of arrows 54, 56. Thus, clean pre-operative pad sections may be quickly substituted for used, glazed sections to provide a consistent pad surface (with a uniform coefficient of friction). In addition, the used, glazed sections may be conditioned at a point downstream from the work piece carrier 30. The conditioned portion may be returned to the work piece carrier 30. A downstream roller (not shown in FIG. 1) draws the glazed post-operative portion of the pad 22 away from the work piece carrier 30.
Although the polishing system 20 is an improvement over the prior art, there is still a need for an improved system for conditioning the pad 22 to increase its useful life and improve its performance. Moreover, there is a need in the art for an improved conditioning device for applying different conditioning treatments to different portions of a polishing pad. The need for an improved conditioning device is applicable to web-shaped and circular polishing pads.
Systems for conditioning polishing pads are described in U.S. Pat. Nos. 5,830,043 (Aaron et al.), 5,785,585 (Manfredi et al.), 5,779,526 (Gill), 5,775,983 (Shendon et al.), 5,655,951 (Meikle et al.), 5,611,943 (Cadien et al.), 5,664,987 (Renteln), 5,527,424 (Mullins), and 5,486,131 (Cesna et al.) and European Published Patent Application No. 770,455 (Ko et al.).
The disadvantages of the prior art are overcome to a great extent by providing a web-format polishing apparatus with a device for conditioning a web-shaped polishing pad. Thus, according to one aspect of the invention, a polishing machine is provided with a system for moving a web-shaped polishing pad to and fro in the longitudinal direction, and a downstream device for conditioning a used glazed portion of the pad. According to this aspect of the invention, after the glazed portion is conditioned, it can be returned to its polishing position to polish more substrates.
In an alternative embodiment of the invention, the polishing pad may remain stationary and the conditioning device may be moved over and/or on the pad to the desired position for conditioning.
The polishing apparatus may be, for example, a chemical-mechanical planarizing machine for processing semiconductor wafers.
The conditioning device is preferably arranged to apply different conditioning treatments to different portions of the glazed polishing pad. Thus, the conditioning device may have roller segments that rotate at different speeds. Alternatively, the conditioning device may have non-cylindrical rollers that provide different rotational speeds at the pad surface, or means for applying different pressures to different portions of the pad.
According to another aspect of the invention, a conditioning device may be moved laterally to provide uniform or blended conditioning despite non-uniformities (such as spaces between rollers) in the conditioning device. In an alternative embodiment of the invention, a conditioning device is located at an angle with respect to the pad to provide uniform or blended conditioning without lateral movement.
The conditioning device may also be moved longitudinally, if desired, to ensure the desired conditioning over the entire length of the glazed portion.
According to another aspect of the invention, the surface characteristics of a polished work piece are measured, and the conditioning device is then controlled or adjusted in accordance with the measured characteristics. Thus, the invention may be used to reduce the occurrence of so-called within-wafer-non-uniformities (xe2x80x9cWIWNUsxe2x80x9d).
Conditioning devices constructed in accordance with the present invention may be used with web-shaped polishing pads and with rigid circular platen pads.
These and other features and advantages of the invention will become apparent from the following detailed description of preferred embodiments of the invention.